Mitsubishi Eclipse 1990-1998 Repair Guide

Heated Oxygen Sensor

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OPERATION



Some late model vehicles utilize two heated oxygen sensors. One mounted in the exhaust manifold, and one threaded into the exhaust pipe.

The heated oxygen sensor, mounted in the exhaust gas flow, is a device which produces an electrical voltage when exposed to oxygen present in the engine exhaust gases. The electrical voltage produced by the oxygen sensor is proportional to the amount of oxygen present in the exhaust and therefore, representative of the air/fuel ratio. The voltage produced by the sensor is sent to the ECM. The ECM will check whether the actual air/fuel mixture ratio is richer or leaner than the optimal (theoretical) ratio, and adjust accordingly. The heated oxygen sensor is electrically heated internally for faster switching during cold engine operation.

If the oxygen sensor has malfunctioned, the driveability of the vehicle may not be influenced. However, hazardous components (HC, CO, NOx) in the exhaust gas will increase.

TESTING



1990-94 2.0L Engine

See Figures 1 and 2

  1. Disconnect the oxygen sensor connector. Connect test harness MD998464 or equivalent, to the sensor harness. If the test harness is not available, perform the test procedure using the sensor harness terminals listed below. The color codes may not be the same on the sensor harness as they are for the test harness.
  2.  



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Fig. Fig. 1: Heated oxygen sensor harness side connector identification-1990-94 2.0L engines



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Fig. Fig. 2: Heated oxygen sensor terminal identification-1990-94 2.0L engines

  1. Measure the resistance across terminals 4 (blue connector of test harness) and 3 (red connector of test harness) of the oxygen sensor test connector or sensor harness. If no continuity, replace the sensor.
  2.  
  3. Start and run the engine until normal operating temperature is reached.
  4.  
  5. Using jumper wires, connect terminals 3 (red connector of test harness) and 4 (blue connector of test harness) of the oxygen sensor harness connector to the battery positive and negative terminals respectively.
  6.  

Be sure to connect the voltmeter to the terminals carefully. Any short circuits could damage the sensor.

  1. Connect a digital voltmeter across terminals 1 (yellow connector of test harness) and 2 (black connector of test harness).While repeatedly racing the engine, measure the output voltage of the sensor.
  2.  
  3. The desired reading is 0.6-1.0 volts. If the reading differs from the desired voltage, replace the sensor.
  4.  

1995-98 Vehicles
2.0L non-turbo engine

See Figures 3 and 4

  1. To test the front heated oxygen sensor, perform the following:
    1. Disconect the heated oxygen sensor connector.
    2.  
    3. Using an digital voltmeter (DVOM), check for continuity (about 12 volts at 68°F) between terminals 3 and 4 on the connector. If there is no continuity, replace the sensor.
    4.  
    5. Start the engine and let run until normal operating temperatures are reached.
    6.  

  2.  


WARNING
When connecting the jumper wires, be very careful, as the sensor can be damaged!

    1. Use jumper wires to connect terminal 3 of the sensor connector to the positive battery terminal and terminal 4 to the negative battery terminal.
    2.  
    3. Connect a digital voltmemter between terminals 1 and 2.
    4.  
    5. While repeatedly racing the engine, measure the voltage. It should be 0.6-1.0 volts. If not, replace the sensor.
    6.  




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Fig. Fig. 3: Testing the front heated oxygen sensor for proper voltage-1995-98 2.0L non-turbo engine

  1. To test the rear heated oxygen sensor, perform the following:
    1. Disconect the heated oxygen sensor connector.
    2.  

  2.  



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Fig. Fig. 4: Check for continuity between terminals 1 and 2 on the rear oxygen sensor-1995-98 2.0L non-turbo engine

    1. Using an digital voltmeter (DVOM), check for continuity (about 12 volts at 68°F) between terminals 1 and 2 on the connector. If there is no continuity, replace the sensor.
    2.  


2.0L turbo and 2.4l engines

See Figures 5, 6 and 7

  1. To test the front heated oxygen sensor, perform the following:
    1. Disconect the heated oxygen sensor connector and attach the special test harness (MD998464 or equivalent) to the connector on the heated oxygen sensor side.
    2.  
    3. Make sure there is continuity (about 12 volts at 68°F) between terminal 1 (red clip) and terminal 3 (blue clip) on the heated oxygen sensor connector. If there is no continuity, replace the sensor.
    4.  
    5. Start the engine and let run until normal operating temperatures are reached.
    6.  

  2.  


WARNING
When connecting the jumper wires, be very careful, as the sensor can be damaged!

  1. Use jumper wires to connect terminal 1 (red clip) on the sensor connector to the positive battery cable and terminal 3 (blue clip) to the negative battery terminal.
  2.  



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Fig. Fig. 5: Testing front heated oxygen sensor connector-1995-98 2.0L turbo and 2.4L engines

  1. Connect a DVOM between terminal 2 (black clip) and 4 (white clip).
  2.  
  3. While repeatedly racing the engine, measure the voltage. It should be 0.6-1.0 volts. If not, replace the sensor.
  4.  



Click image to see an enlarged view

Fig. Fig. 6: Checking for proper sensor voltage-1995-98 2.0L turbo and 2.4L engines

  1. To test the rear heated oxygen sensor, perform the following:
    1. Disconect the heated oxygen sensor connector.
    2.  

  2.  



Click image to see an enlarged view

Fig. Fig. 7: Testing the rear oxygen sensor continuity-1995-98 2.0L turbo and 2.4L engines

    1. Using an digital voltmeter (DVOM), check for continuity (about 12 volts at 68°F) between terminals 3 and 4 on the connector. If there is no continuity, replace the sensor.
    2.  


REMOVAL & INSTALLATION



See Figures 8, 9 and 10


CAUTION
The oxygen sensor, exhaust system and surrounding components become very hot during engine operation. Avoid personal injury by waiting for a cooled motor or wearing protective clothing and gloves.

  1. Disconnect negative battery cable.
  2.  



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Fig. Fig. 8: Use a wrench or an oxygen sensor socket to loosen the sensor



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Fig. Fig. 9: Some models also use a second oxygen sensor threaded into the exhaust pipe near the catalytic converter



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Fig. Fig. 10: Once loosened, remove the sensor from the exhaust pipe

  1. Raise and safely support the vehicle.
  2.  
  3. Remove the oxygen sensor from the exhaust manifold, or exhaust pipe, as applicable.
  4.  

To install:
  1. If not already done, coat the threads of the replacement sensor with anti-seize compound. New sensors are already coated with the substance. Take great care not to contaminate the oxygen sensor probe with the anti-seize compound.
  2.  
  3. Install the oxygen sensor into the exhaust manifold or pipe, as applicable. Tighten the sensor to 33 ft. lbs. (45 Nm).
  4.  
  5. Reconnect the wiring harness to the sensor. Connect the negative battery cable.
  6.  

 
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